The present invention relates to a linear drive comprising a housing which has a longitudinal slot, a drive part able to be moved longitudinally in the housing, a longitudinal guide arranged outside the housing and extending parallel to the direction of movement of the drive part, on which a guide part, suitable for connection with a load, in arranged for movement along a guide path in the longitudinal direction, and a link means connecting the drive part with the guide part with the formation of a common longitudinally moving unit and extending through the longitudinal slot.
Linear drives of this type are termed slotted cylinders and are described in, for instance, the European patent publication 0 113, 790 B1, the European patent publication 0 157 892 B1 or the German patent publication 3,124,915 C2. In such designs the drive part is constituted by a piston, which is moved by the action of a drive fluid. The carriage-like guide part is moved synchronously on displacement of the drive part as a consequence of the coupling via the link means. It serves for connection with a load and to join the drive with moving loads. Owing to the external longitudinal guide for the guide part the drive part is practically not subjected to external factors likely to cause wear.
In the case of the known linear drives the guide part is mounted externally on the housing containing the drive part, straddles the slotted part of the housing and bears on either side of the slot directly on guide tracks shaped or formed directly on the outer periphery of the housing. Although the straddling of the slotted part of the housing prevents splaying of the housing when it is subjected to a high internal pressure, there are substantial transverse forces adjacent to the guiding contact, which may lead to jamming and an impairment in function, and at least to more rapid wear of the guide components. Jamming may, it is true, be substantially prevented if sufficient play is provided adjacent to the guide contact, but apart from the loss of a straddling effect, this means that accuracy of guiding is less satisfactory. In the case of a guide part heavily loaded by an object to be conveyed erratic movements may even effect the drive part, for which reason in the European patent publication 0 113, 790 B1 or the European patent publication 0 157 892 B1 intermediately arranged couplings are provided, which isolate the guide part from the drive part to a certain degree. Apart from these shortcomings the manufacture of the guide tracks on the housing is elaborate and when wear takes place it is difficult to repair the guide tracks.